Depending upon your circumstances, you may need to use:
<div style="text-align: center; width: 100%">
The differences (from previous answer):
- using CSS style instead of old attribute methodology. Images are normally handled like text with respect to alignment.
- the width:100% forces div to take entire width of it's container and map will be centered in that space. Otherwise, it will center in div but not on page.
If you have other items in-line with the image than you either have to take their widths into account (and center the div containing the image) or consider using z-index styles in order to layer the items.
A further consideration - you could also consider sizing your div with a specific width and then aligning it via style='margin:0px auto 0px auto;'